FUNDAMENTAL STUDY ON REMOTE MONITORING OF SHIP STRUCTURES BY USING FIBER-OPTIC SENSORS

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Ships and offshore structures are occasionally damaged by rough waves and strong winds. It is not easy to estimate loads of waves and winds to the marine structure because of the statistical feature of oceanographic phenomena. Landing and collision of ships might result in severe marine pollution. Prevention of serious damage of the marine structures might be achieved by monitoring the loading condition and by inspecting the structural integrity. The concept of smart structures with fiber-optic sensor network can be applied to the marine structures.There are plenty of marine structures in huge dimensions, for example, overall length of very large crude carrier (VLCC) exceeds 200 m. Displacement sensor with long gauge length is suitable for global uderstanding of structural ship behavior. New long gauge length sensor, which has simple sensor head and achieves high sensitivity, should be developed for smart marine structure. A fiber-optic Laser-Doppler vibrometer (FLDV) sensor has been proposed as the alternative sensor in the present study. In the present study, applicability of the fiber-optic Laser-Doppler sensor to ship structures is discussed.Fiber Bragg Grating (FBG) was applied as quasi-distributed strain sensor and accuracy and stability of sensing function was investigated and applied to model specimen subjected to flexural load. International America's Cup Class (IACC) yachts are specific boats whose most components made of carbon fiber reinforced plastic (CFRP) and that are regulated by the IACC rule. A Brillouin optical time domain reflectometer (BOTDR) is a fiber optic distributed sensor that can measure strain and temperature along an optical fiber. We equipped IACC yachts that were the Japanese entry in America's Cup 2000 with these sensors. Strain distributions of the yachts measured with BOTDR were used for structural health monitoring and assessments of the structural integrity were continued during races.